The present invention relates generally to a vane type gas compressor, and in particular to a vane type gas compressor used for air conditioners for automobiles.
As conventional vane type gas compressors, for example, there are those in which a front side block, a rear side block, a cylinder, a rotor and vanes which constitute the compressor main body are made of aluminum alloys, a rotor shaft is made of a hardened steel material such as an SCM material or the like, and CFC-12 (dichlorodifluoromethane; CCl.sub.2 F.sub.2) is used as a refrigerant.
In such a vane type gas compressor, the rotor shaft is maintained in a plain bearing, wherein both ends of the rotor shaft are supported in a manner freely capable of rotation by means of bearing portions provided at boss portions at the centers of the front side block and the rear side block, respectively. The lubrication at the bearing portions has been usually performed by blowing lubricating oil under a high pressure from an oil reservoir in the rear space of a casing, or by using lubricating oil dissolved in CFC-12 refrigerant. In addition, lubrication has been also performed by the lubricating action of the CFC-12 itself.
However, CFC-12, which is used for the conventional vane type gas compressor, contains chlorine as a component, and this chlorine destroys the ozone layer, so that the use of CFC-12 as a refrigerant for automobile air conditioners will be prohibited in the future.
Therefore, an alternative refrigerant is necessary, and for this purpose, it is considered that a refrigerant containing no chlorine is used. However, the chlorine itself is an element having good lubricating action, so that on the contrary, when a refrigerant containing no chlorine is used, its lubricating property is inferior to that of CFC-12.
For example, when the compressor is stopped under an operating condition in which a relatively small amount of lubricating oil is in the oil reservoir in the rear space of the casing, and this condition is left for a long time, such a state occurs that the lubricating oil is diluted by the liquid refrigerant, and the lubricating oil at the bearing portion is washed out by the liquid refrigerant. When the compressor is started from this state, the bearing portion temporarily is in a no-oil feeding state, however, when the refrigerant containing no chlorine is used, the lubricating action of the refrigerant itself cannot be expected at all, so that there is a fear to cause a new problem that cohesion takes place due to the mutual sliding contact between metals of the rotor shaft of the iron series metal and the bearing surface of the aluminum alloy, resulting in seizure.